Apparatus for coating cathodes



Nave. 18, 1947. R. o. MORSE APPARATUS FOR COATING CATHODES P/MMEWI' (04776 a BBew/rme; 2157 BY MM ATTORNE Patented Nov. .18, 1947 2,431,135 APlfARATUS FOR COATING CATHODES Rupert 0. Morse,- Hamilton,-

Westinghouse Electric Corporation, urgh, Pin, a corporation of Pennassignor to East Pitts sylvania Ontario, Canada,

Application March 29, 1944, Serial No. 528,565

3 Claims. (oi. 91-46) The present invention relates to discharge devices and more particularly to an apparatus for coating electrodes therefo In the most common form of discharge devices now on the market the electrodes usually comprise rather closely wound coiled-coil filaments coated with a material such as an alkaline earth oxide to render them electron emissive at relatively low temperature. Moreover, it is this electron emissive coating which is the most salient factor in the life 01 the device since failure occurs once the coating is lost from the electrode.

The manner of application of. this electron emissive coating heretofore employed in the art comprises dipping the mounted coiled-coil filament in a suspension of solids. The latter usually consists of a carbonate of the alkaline earths, such as barium, strontium, etc., which are readily converted to the OXide on heating, and suspended in a solution of cellulose esters and a suitable solvent as acetate esters. shown that a large amount of coating is preferable to a small amount, since the larger the quantity the longer the life of the device, provided the coating is tenaciously retained by the refractory metal electrode. However, the simple concentration of the emissive material to give the electrode a heavier coat has definite limitations.

This is because a concentration of the material in suspension renders the latter too viscous so that it fails to penetrate to the core of either the primary or secondary on the periphe y of the coils from which it is easily dislodged by mechanical shock as well as by positive ion bombardment during operation of the device. n the other hand reduction of the viscosity sumciently to cause pentration of the suspension into the core of the windings during dipping results in the deposit being below the optimum for maximum life.

It is accordingly the primary object of the present invention to provide an apparatus for coating an electrode "for a discharge device in which the electron emissive coating extends over substantially the entire surface area of the electrode and particularly into the core of the primary and secondary windings.

A further object of the present invention is the provision of apparatus for stretching the filamentary electrode for a discharge device during the application of an electron emissive coating thereto so that the coating material forms a tenacious bond with substantially the entire surface area of the electrode and particularly penetrates into the core of the filamentary windings.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Exhaustive tests have windings and is held chiefly Figure 1 is an elevational view partly in section, of an apparatus which may form a part of the customary indexing machine used in manuiacture of a discharge device and operable to apply an electron emissive coating to the electrode in accordance with the present invention,

Figure 2 is a prospective view of the usual type electrode mount used in certain types of discharge devices prior to its coating step as shown in Fig. 1,

Figure 3 is a fragmentary view partly in section of the uncoated filamentary electrode together with the stretching arm portion or the-apparatus of Fig. 1, v

Figure t is a fragmentary view partly in section similar to Fig. 3 but showing an electrode in its stretched coating position, and

Figure 5 is a side in Fig. 4.- during its stretched coating position.

Referring now to the drawing in detail an electrode mount 5 for a discharge device such as a fluorescent lamp is shown in Fig. 1 suspended from mount holders 5 forming part'of the customary automatic mounting machine. Inasmuch as such machine per se forms no part of the present invention it is believed unnecessary to describe the same in detail. It should suffice to say that such machine is provided with a head which indexes the mounts to various positions during their fabrication, one position in accordance with the present invention being that of coating the electrode, as shown in this Fig. 1. Such machine is provided with a supporting bracket i having a pair of projecting arms 8 with each arm provided with a bearing 9 in which is iournalled a shaft i t.

A cup i2 is rigidly secured to the upper end of the shaft it, such as by a set screw or the like.

it, which holds a relatively viscous suspension of electron emissive material It such as barium or strontium carbonate as previously mentioned. In order to rotate the shaft. It together with the cup it, a gear is is secured to the shaft in, such as by a set screw or the like It, with this gear iii meshing with a driving gear ll operatedby the customary automatic mounting machine mechanism. A cam is secured to a shaft I9 and also operated by the machine mechanism serves to raise and lower the shaft ill and cup H to permit movement of the coated electrode mount out of position an an unccated electrode mount into position during indexing of the machine, so as to dispose the electrode approximately in the center of the cup it with the lowermost portion of the coils slightly above the level of the suspension it when the cup is raised, as shown in Hg. 1, to its normally fixed position. A stationary paddle or the like 20 is immersed in the material it for the purpose of causing a slight agitation of the latter.

A pivqifid ball-crank 2| is supported by the view of the electrode as shown bracket 1 to which is detachably secured an arcuate stretching arm 22 in the form of a wire or rod and having a substantially semi-circular end 23 simulating the radius of the coiled filament carried by the mount 5. Also supported by the bracket 1 is a solenoid 24 the core 25 of which is connected by a pivoted link 26 to the bellcrank 2|. The winding of this solenoid 24 is periodically energized from a suitable source forming a part of the customary automatic mounting machine mechanism and so synchronized with indexing of the machine that energization occurs only when the uncoated electrode is centered over the cup l2.

By reference to Fig. 2 it will be noted that the electrode mount comprises a flare tube 21 hav- 28 in which is hermetically sealed a pair of leading-in conductors 29 and 30 and the usual exhaust tube 32 is provided for evacuation of the completely assembled device. On the electrode side of the press these conductors are bent laterally and spaced substantially parallel to each other as shown and function in the well known manner as anodes during one half wave of the alternating current cycle. The coiled-coil tungsten filament constitutlng the cathode 33 is suspended between the leading-in conductors 29 and 30 with the axis of the coils substantiallyparallel with the anode forming portions of such conductors.

During fabrication the electrode mount with its uncoated electrode 33 is held in an inverted position in the machine, and after it is indexed to the position above the cup 12 and the latter is raised by cam l8 to its normally fixed position, as shown by the full lines in Fig. 1, the solenoid 24 is next energized. This raises the core 25 of the solenoid. to the proper height, as regulated by an adjustable stop 34, causing counter-clockwise movement of the bell-crank 2| about its pivot with attendant downward movement of the arcuate stretching arm 22 in the direction indicated by the arrow in Fig. 2. The semi-circular end 23 accordingly will engage the filamentary cathode 33 substantially at the center thereof thus pushing the middle of the cathode 33 below the surface of the adjacent emissive material l4 within the cup l2.

As will be noted from Figs. 4 and 5, this stretches or elongates the filamentary cathode to approximately 150% of its normal length without causing any perceptible permanent deformation. The attendant separation of the helices insures complete penetration of the viscous emissive material to the core of the primary windings and its subsequent contraction, upon disengagement of the stretching arm 22, likewise results in the trapping of a relatively large quantity of "the emissive material in the core of the secondary windings so that a heavy deposit of tenaciously held emissive material is obtained.

It thus becomes obvious to those skilled in the art that a method and apparatus for coating a cathode for a discharge device is provided by the present invention wherein a relatively heavy deposit of electron emissive material is applied which penetrates to the cores of the primary and secondary windings where it is tenaciously held despite mechanical shock and positive ion bombardment to which the completed device may be subjected during usage. Moreover, tests have conclusively shown that devices and particularly fluorescent lamps employing ele tlqdes made in accordance with the present invention have resulted in a considerably longer useful life than heretofore attainable with electrodes of the prior art. It should also be obvious that while the present invention has been herein shown and described particularly in connection with the electrode for a discharge device such as a fiuorescent lamp, it is equally applicable to the electrode of other types of discharge devices, such as high pressure discharge lamps, radio tube electrodes, and the like.

Although one specific embodiment of the resent invention has been shown and described it is to be understood that still further modifications thereof may be made without departing from the spirit and scope of the appended claims.

I claim:

1. An apparatus for applying an electron emissive coating to the coiled filament for an electrical energy translation device comprising a receptable for holding said coating materialand movable into and out or a normally fixed position, means for supporting said coiled filament slightly above the surface of the coating material when said receptacle is in-its normally fixed position, and means operable to engage said coiled filament and distort-the coils thereof below the surface of said coating material with simultaneous expansion of said coils to cause penetration of the coating material to the core of the latter.

2. An apparatus for applying an electron emissive coating to a coiled filamentary electrode of a discharge device comprising a receptacle for holding said coating material and movable into and out of a normally fixed position, a support for said coiled filamentary electrode suspended from its leading-in conductors and operable to position an electrode slightly above the surface of the coating material when said receptacle is in its normally fixed position, and a stretching arm operable to contact said filamentary electrode and force the coils thereof below the surface of said coating material to cause penetration of the coating material to the core ofthe latter.

3. An apparatus for applying an electron emissive coating to the coiledfilament for an electrical energy translation device comprising a receptacle for holding said coating material, means for supporting said coiled filament above the surface of the coating material within said receptacle, and means movable into engagement with said filament and operable to distort the filament coils beneath the surface of the coating material with attendant expansion thereof to cause penetration of the coating material to the core of the coils.

RUPERT o. MORSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 781,025 Rupley Jan. 31, 1905 1,519,085 Barry et al Dec. 9, 1924 1,953,799 Eaton Apr. 3, 1934 2,329,024 :Albright Sept. '7, 1943 2,251,046 Gaidies et al July 9, 1941 1,329,467 Miskella Feb. 3, 1920 

